This invention relates to a catalyst and a solid catalyst component for preparing polyolefins having a broad molecular weight distribution and a high stereoregularity, particularly, polypropylene or its copolymer thereof, in high yields.
A number of proposals have been made on an olefin polymerization catalyst and a solid catalyst component for preparing polyolefins which permit olefins to be subject to polymerization or copolymerization in the presence thereof. The solid catalyst component conventionally mainly consists of a titanium halide, a magnesium compound and an electron donor compound and the catalyst includes a combinaiton of the solid catalyst component, an organic aluminum compound, a silicon compound and the like.
For Example, Japanese Patent Application Laid-Open Publication No. 3010/1988(63-3010) and the U.S. Pat. No. 4,829,037 assigned to the same assignee as the present application propose an olefin polymerization catalyst which comprises a solid catalyst component (A) prepared by contacting dialkoxy magnesium, a diester of an aromatic dicarboxylic acid, an aromatic hydrocarbon and titanium halides with one another to obtain a product and subsequently subjecting the product to a heating treatment in the powdered state; an organic alumium compound (B); and an organic silicon compound (C). The Japanese patent provides examples directed to a process for polymerizing olefins in the presence of the catalyst.
Japanese Patent Application Laid-Open Publication No. 154705/1988 (63-154705) proposes an olefin polymerization catalyst which comprises a solid catalyst component (A), an organic aluminum compound (E) and a silicon compound (C) and provides examples directed to a process for polymerizing olefins in the presence of the catalyst. The catalyst component (A) for use in the catalyst is prepared by adding titanium tetrachloride to a mixed solution containing a magnesium compound obtained by reacting a magnesium powder with alkylmonohalides in the presence of iodine, tetraalkoxy titanium, aliphatic hydrocarbon and aliphatic alcohol to precipitate a solid substance and adding a diester of phthalic acid thereto to obtain a solid product. The solid product is then brought into contact with titanium tetrachloride in the presence of aromatic hydrocarbon.
U.S. Pat. No. 4,816,433 proposes a solid catalyst component prepared by contacting titanium tetrachloride with a suspension formed of diethoxy magnesium and alkyl benzene, adding a diester of phthalic acid to permit a reaction to be carried out therebetween, to thereby obtain a solid product, and then subjecting the solid product to a contact reaction with titanium chloride in the presence of alkyl benzene, as well as a catalyst for polymerization of olefins comprising the solid catalyst component thus produced, and an organic aluminum compound and an organic silicon compound.
Japanese Patent Application Laid-Open Publication No. 315406/1989 (1-315406) and the U.S. Pat. Nos. 4,970,186 and 5,130,284 propose an olefin polymerization catalyst which comprises a solid catalyst component (A) prepared by forming a suspension of diethoxy magnesium and alkyl benzene, contacting the suspension with titanium tetrachloride and adding a diester of phthalic acid thereto to obtain a solid product which is recovered and washed with alkyl benzene. Subsequently the solid product is brought into contact with titanium tetrachloride in the presence of alkyl benzene, an organic aluminum compound, and an organic silicon compound to prepare the catalyst. The Japanese patent also discloses examples directed to a process for polymerizing olefins in the presence of the catalyst.
Also, U.S. Pat. No. 4,927,797 proposes a catalyst system for olefin polymerization comprising a catalyst component obtained by contacting dialkoxy magnesium, an aromatic hydrocarbon, titanium tetrachloride and a diester of an aromatic dicarboxylic acid with each other, an organic aluminum compound, and an organic silicon compound containing a single cycloalkyl group.
Further, U.S. Pat. No. 4,990,479 proposes a catalyst for olefin polymerization comprising a solid titanium catalyst component, an organoaluminum compound, and a specific organosilicon compound containing a cyclopentyl group, a cyclopentenyl group, a cyclopentadienyl group or a derivative derived from any of these groups. Also, the U.S. patent proposes an olefin polymerization method using the catalyst.
The foregoing catalysts exhibit a degree of activity sufficient to permit elimination tile deashing which removes catalyst residues such as chlorine, titanium and the like remaining in a polymer such as polypropylene or its co-polymer produced, as well as to improve yields of a stereoregular polymer and increase the activity of the catalyst during polymerization. While these catalysts have provided the foregoing benefits, the polyolefins such as polypropylene its co-polymer obtained using these catalysts comprising the highly active catalyst component, organic aluminum compound and silicon compound have a narrow molecular-weight distribution as compared with polyolefins prepared by using the conventional olefin polymerizing catalyst which comprises the titanium trichloride based catalyst component, an organic aluminum compound and an electron donor compound which is added as required. The narrowed molecular-weight distribution causes the formability or moldability of the polyolefin to deteriorate, resulting in some restrictions on the polyolefin's applications. Thus, it is desirable to develop a catalyst for providing a polymer having a broad molecular weight distribution.
Furthermore, it is highly demanded to realize weight-saving of plastics used for automobiles, domestic electric appliances and the like in order to save energy and resources in view of global environment protection recently advocated. In order to solve the problem, it is required to decrease a thickness of the plastics while ensuring strength of the plastics such as impact resistance and the like. Also, In association with the problem, an improvement in crystallinity of resin to increase rigidity of the resin is demanded together with an improvement in molecular weight distribution described above. Concurrently, it is desirable to provide a catalyst for preparation of a polymer exhibiting improved crystallinity.
Various approaches have been tried to improve the molecular weight distribution including the multi-stage polymerization process which provides polyolefins of increased molecular-weight distribution. However, the multi-stage polymerization requires a complicated polymerization operation repeatedly and requires a troublesome treatment for recovering the chelating agent used during the polymerization, which increases the cost of the polymerization process.
In view of the above, Japanese Patent Application Laid Open Publication No. 7703/1991 (3-7703) proposed a process for polymerizing olefins In the presence of an olefin polymerizing catalyst comprising a solid titanium catalyst component consisting essentially of magnesium, titanium, halogen and an electron donor compound; an organic aluminum compound; and two types of organic silicon compounds serving as the electron donor. The Japanese patent states that the proposed polymerization process eliminates the need for the troublesome multi-stage polymerization process as described above and provides polyolefins of a molecular-weight increased to an intended degree. However, the proposed process likewise renders the polymerization operation troublesome because it requires the use of two types of organic silicon compounds as the electron donor.
Accordingly, a need continues to exist for a polymerization process which produces polyolefins with a broad molecular weight distribution at high levels or catalyst activity.
Also, in connection with high crystallinity and high rigidity, polypropylene resin for a high rigidity molded product is proposed in U.S. Pat. No. 4,522,994. However, a catalyst used for preparation of the product proposed in the U.S. patent comprises an improvement of titanium trichloride obtained by reacting titanium tetrachloride with an organic aluminum compound and is substantially decreased in activity as compared with a catalyst of the high-activity type.
Further, U.S. Pat. No. 5,194.531 proposes a method for polymerizing olefins using a catalyst comprising a solid catalyst component of the high-activity type, an organic aluminum compound, and a specific organic silicon compound containing a hydrocarbon group of which a carbon atom attached to a silicon atom is a tertiary carbon atom, to thereby prepare olefin polymers with a broad molecular weight distribution with high yields.
However, the U.S. patent merely suggests that the above-described method for preparation of polyolefins provides olefin polymers with a broad molecular weight distribution with high yields and therefore falls to refer to an improvement in crystallinity of the polymers obtained and its rigidity. Thus, it is highly desirable to develop a catalyst component and a catalyst each of the high-activity type for preparation of polymers which are capable of concurrently solving the above-described two problems or exhibiting a broad molecular weight distribution and high crystallinity.